title: Colonization of Pythium oligandrum in the tomato rhizosphere for biological control of bacterial wilt disease analyzed by real-time PCR and confocal laser-scanning microscopy.
abstract: It recently has been reported that the non-plant-pathogenic oomycete Pythium oligandrum suppresses bacterial wilt caused by Ralstonia solanacearum in tomato. As one approach to determine disease-suppressive mechanisms of action, we analyzed the colonization of P. oligandrum in rhizospheres of tomato using real-time polymerase chain reaction (PCR) and confocal laser-scanning microscopy. The real-time PCR specifically quantified P. oligandrum in the tomato rhizosphere that is reliable over a range of 0.1 pg to 1 ng of P. oligandrum DNA from 25 mg dry weight of soil. Rhizosphere populations of P. oligandrum from tomato grown for 3 weeks in both unsterilized and sterilized field soils similarly increased with the initial application of at least 5 x 10(5) oospores per plant. Confocal microscopic observation also showed that hyphal development was frequent on the root surface and some hyphae penetrated into root epidermis. However, rhizosphere population dynamics after transplanting into sterilized soil showed that the P. oligandrum population decreased with time after transplanting, particularly at the root tips, indicating that this biocontrol fungus is rhizosphere competent but does not actively spread along roots. Protection over the long term from root-infecting pathogens does not seem to involve direct competition. However, sparse rhizosphere colonization of P. oligandrum reduced the bacterial wilt as well as more extensive colonization, which did not reduce the rhizosphere population of R. solanacearum. These results suggest that competition for infection sites and nutrients in rhizosphere is not the primary biocontrol mechanism of bacterial wilt by P. oligandrum.
authors.affiliation: National Agricultural Research Center for Hokkaido Region, Kasaigun, Hokkaido, Japan. stake@affrc.go.jp
authors.forename: Shigehito
authors.initials: S
authors.lastname: Takenaka
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sekiguchi
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Nakaho
authors.forename: Motoaki
authors.initials: M
authors.lastname: Tojo
authors.forename: Akira
authors.initials: A
authors.lastname: Masunaka
authors.forename: Hideki
authors.initials: H
authors.lastname: Takahashi
mesh_terms: D000898:Antibiosis; D001483:Base Sequence; D021903:DNA, Ribosomal Spacer / Q000032:analysis / Q000235:genetics; D054884:Host-Pathogen Interactions; D018551:Solanum lycopersicum / Q000382:microbiology*; D018613:Microscopy, Confocal / Q000379:methods; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology; D018517:Plant Roots / Q000382:microbiology*; D016133:Polymerase Chain Reaction / Q000379:methods; D011775:Pythium / Q000235:genetics / Q000502:physiology*; D043368:Ralstonia solanacearum / Q000502:physiology; D012689:Sequence Homology, Nucleic Acid
chemical_list: D021903:DNA, Ribosomal Spacer